Stent with variable features to optimize support and method of making such stent

ABSTRACT

An intravascular stent especially suited for implanting in curved arterial portions or ostial regions. The stent can include an end region which is fabricated to have a greater radial strength than the remaining axial length of the stent. Such a stent is particularly suited for use in ostial regions, which require greater support near the end of the stent. The stent alternatively can include sections adjacent the end of the stent with greater bending flexibility than the remaining axial length of the stent. Such a stent is particularly suited for use in curved arteries. The stent can also be constructed with an end that has greater radial strength and sections adjacent the end with greater bending flexibility. Such a stent prevents flaring of the stent end during insertion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.09/599,158 filed Jun. 21, 2000, which is a continuation of applicationSer. No. 09/040,145 filed Mar. 17, 1998 (now U.S. Pat. No. 6,676,697),which is a division of application Ser. No. 08/716,039 filed Sep. 16,1996 (now U.S. Pat. No. 5,807,404).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to stents for implanting into aliving body. In particular, the present invention relates tointraluminal stents especially suited for implanting in a variety oflumens having variable characteristics, such as variable curvature, sidebranching, variable diameter, variable wall compliance or “end effects”of either the lumen, as found, e.g., in ostia, or the stent as theparameters may change at its ends.

2. Description of the Prior Art

It is well known to use a stent to expand and impart support todifferent bodily conduits, such as blood vessels, by expanding atube-like structure inside the vessel requiring support against collapseor closure. U.S. Pat. No. 5,449,373 shows a stent preferably used forvascular implantation as part of a balloon angioplasty procedure. Thestent of U.S. Pat. No. 5,449,373 may be delivered through, or implantedin, a curved vessel. One shortcoming of conventional stents is that theymay have deficiencies due to “end effects” where the ends of the stenttend to “flare out” during insertion or after expansion or have adecreased radial force at the end. Still another shortcoming ofconventional stents is they do not have different characteristics,(e.g., flexibility and rigidity), to accommodate any changingcharacteristics of the section of the lumen requiring different stentcharacteristics.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention provides for various embodiments of anintraluminal stent which includes varied or different mechanicalproperties along the axial length of the stent in order to improve stentend effects, or to accommodate variable vessel features. As a result,the various embodiments of the present invention allow for variableproperties such as flexibility or radial support between axial regionsof the stent. These varied properties can be accomplished in a number ofdifferent ways, including decreasing or increasing the thickness orwidth of elements of one or more of the sections relative to othersections and/or increasing or decreasing the axial length of one or moreof the sections and/or changing the cell shape and size and/or changingmaterial properties (e.g., strength, elasticity, etc.) of the materialin one section relative to other sections.

The various embodiments of the stents of the present invention may beadapted to provide more flexibility at the ends to allow the stent toaccommodate the curvature of a vessel in which the stent is implanted.The degree of flexibility and the distance from the end of the stent towhich the extra flexibility is imparted may be varied as specificapplications dictate. This flexibility at the ends reduces the chance ofa potential trauma point being created in the vessel by the stent tippressing on the wall outside of the curve if the stent is not flexibleenough along its longitudinal axis. In one embodiment of the presentinvention, flexibility of the stent ends is increased by reducing thegauge of the material used in a section or sections at the stent ends.In another embodiment the flexibility of the stent ends is increased bychanging the dimensions of a section or sections at the stent ends. Inyet another embodiment of the invention, the flexibility of the stentends is increased by changing both the dimensions and the gauge of thematerial used in a section or sections at the stent ends.

The various embodiments of the stents of the present invention may alsobe adapted to insure increased radial strength at the ends. Radialstrength is the resistance of a section of the stent, in an expandedstate, to radial contraction. Increasing the radial strength of a stentat the ends is particularly advantageous for stents supporting ostia.Because lesions at an ostium tend to be more calcified or hardened, andtherefore require more support, the section of the stent supporting theostium must be relatively strong. It is also the case that a stent withuniform characteristics has a decreased radial force at the end due tothe “end effect” whereby the last row has no support on one side. In oneembodiment of the present invention, the strength of the stent at theend supporting, e.g., the ostium, is increased by reducing the length ofsome sections at the stent end.

The various embodiments of the stent of the present invention alsoreduce the chance of “flare” at the end of the stent while the stent isbeing fed into a vessel. During insertion of the catheter deliverysystem into a curved vessel, the delivery system, including the stentcrimped on it, bend along the curvature of the vessel. This bending ofthe stent can cause a “flaring out” of the leading edge of the stent.This flaring could cause the stent to catch on the surface of the vesselwhich could result in trauma to the vessel, could inhibit furtherinsertion and proper positioning in the target area, and could causeplaque to break off, which could embolize and clog the vessel. In oneembodiment of the present invention, flare is minimized by making thesection at the stent end stronger by reducing its length, and by makingsections adjacent to the stent end more flexible by reducing theirwidths, thus, decreasing the bending strength of those sections. Bendingstrength is the resistance of a section of the stent to axial bending.As a result, the end of the stent remains tightly crimped on theballoon, and the bending moment is taken up by the deformation of themore flexible sections. Upon expansion, the reduced bending strengthallows the end of the stent to curve and fit better the curvature of thevessel, thereby, reducing the pressure of the tip of the stent on theinternal wall of the vessel being treated.

It is an object of this invention to provide a stent which does not havesharp points or protrusions at its end concentrating pressure on thevessel's wall upon expansion of the stent in a curved portion of avessel.

It is another object of this invention to provide a stent having aradial force at its distal end that is greater than the radial force inthe portion of the stent proximal to the distal end.

It is yet another object of this invention to provide an expandablestent, comprising: a plurality of interconnected flexible cells defininga stent having a proximal end and a distal end and a longitudinal axis,the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with a distal rowdisposed at the distal end of the stent and a proximal row disposed atthe proximal end of the stent, wherein the cells disposed in the distalrow of the stent are adapted to exert greater radial force and arefurther adapted to be more flexible than the cells disposed in the rowsdisposed between the distal row and the proximal end of the stent.

It is still another object of this invention to provide an expandablestent, comprising: a plurality of interconnected flexible cells defininga stent having a proximal end and a distal end and a longitudinal axis,the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with a distal rowdisposed at the distal end of said stent and a proximal row disposed atthe proximal end of the stent, wherein the cells in the distal row ofthe stent and the cells disposed in the proximal row of the stent areadapted to exert greater radial force and are further adapted to be moreflexible than the cells disposed in the rows disposed between the distalrow and the proximal row.

It is another object of this invention to provide an expandable stent,comprising: a) a plurality of interconnected flexible cells defining astent having a proximal end and a distal end and a longitudinal axis,the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with a distal rowdisposed at the distal end of the stent and a proximal row disposed atthe proximal end of the stent, each of the flexible cells comprising afirst member, a second member, a third member, and a fourth member; b) afirst C-shaped loop disposed between the first member and the thirdmember; c) a second C-shaped loop disposed between the second member andthe fourth member; d) a first flexible connector disposed between thefirst member and the second member; and e) a second flexible connectordisposed between the third member and the fourth member, wherein thecells of the distal row are provided with first and third members thatare shorter than the second and fourth members in the distal row, andwherein the distal row is provided with first and second flexibleconnectors that are more flexible than the flexible connectors in thecells in the other rows of the stent.

It is yet another object of this invention to provide an expandablestent, comprising: a) a plurality of interconnected flexible cellsdefining a longitudinal stent having a proximal end and a distal end anda longitudinal axis, the cells arranged in a plurality of interconnectedflexible rows disposed along the longitudinal axis of the stent with adistal row disposed at the distal end of the stent and a proximal rowdisposed at the proximal end of the stent, each of the flexible cellscomprising a first member, a second member, a third member, and a fourthmember; b) a first C-shaped loop disposed between the first member andthe third member; c) a second C-shaped loop disposed between the secondmember and the fourth member; d) a first flexible connector disposedbetween the first member and the second member; and e) a second flexibleconnector disposed between the third member and the fourth member,wherein the cells of the distal row are provided with first and thirdmembers that are shorter than the second and fourth members in thedistal row, and wherein the distal row, and the row proximal to thedistal row, are provided with first and second flexible connectors thatare more flexible than the flexible connectors in the other rows of thestent.

It is a further aspect of this invention to provide an expandable stentcomprising: a) a plurality of flexible cells defining a stent having aproximal end and a distal end and a longitudinal axis, the cellsarranged in a plurality of flexible rows along the longitudinal axiswith a distal row disposed at the distal end of the stent and a proximalrow disposed at the proximal end of the stent, each of the flexiblecells comprising a first member, a second member, a third member, and afourth member; b) a first C-shaped loop disposed between the firstmember and the third member; c) a second C-shaped loop disposed betweenthe second member and the fourth member; d) a first flexible connectordisposed between the first member and the second member; and e) a secondflexible connector disposed between the third member and the fourthmember, wherein the cells of the distal row are provided with first andthird members that are shorter than the second and fourth members in thedistal row, and wherein the cells of the proximal row are provided withsecond and fourth members that are shorter than the first and thirdmembers in the proximal row, and wherein the distal row, and the rowproximal to the distal row, and the proximal row and the row distal tothe proximal row are provided with first and second flexible connectorsthat are more flexible than the flexible connectors in the other rows ofthe stent.

It is yet another object of this invention to provide an expandablestent, comprising: a plurality of flexible cells defining a stent havinga proximal end and a distal end, the stent provided with means forimparting a radial force at its distal end that is greater than theradial force in the portion of the stent proximal to the distal end.

It is yet a further object of this invention to provide an expandablestent, comprising: a plurality of flexible cells defining a stent havinga proximal end and a distal end, the stent provided with means forimparting a radial force at its proximal and distal ends that is greaterthan the radial force of that portion of the stent disposed between theproximal and distal ends.

It is another object of this invention to provide an expandable stentfor treating a lumen having a unique characteristic along a portion ofthe lumen, comprising: a plurality of interconnected flexible cells, thecells arranged in a plurality of interconnected flexible rows defining astent having a proximal end and a distal end and a longitudinal axis,wherein at least one of the rows is adapted to accommodate the uniquecharacteristic of that portion of the lumen in contact with the adaptedrow or rows.

It is yet another object of this invention to provide a single flexiblestent with a unibody or one-piece construction which is capable ofimparting support to a lumen or vessel along the entire length of thestent and in which portions of the stent are adapted or modified so asto have characteristics, e.g., bending strength or radial strength, thatare different than the characteristics or features in the rest of thestent along it's longitudinal axis or about its circumference. Thechange in stent features will either accommodate non-uniformity in thetreated lumen or may create different environmental conditions indifferent areas in the lumen. Non-uniformity in a treated vessel can beof many different types such as an ostium, change in diameter, change incurvature, non-continuous cross-section such as triangular or square, ornon-uniformity in surface nature, etc. To accommodate suchnon-uniformity, portions of the stent may be adapted to provide changingdimension, flexibility, rigidity, size of cells, shape of cells, andresponse to pressure as dictated by specific applications. Specificapplications may dictate, e.g., a desired higher radial force at one endwhile the other portions of the stent provide a substantially continuoussupport to the vessel wall with the gaps in the stent sized small enoughto reduce the likelihood of tissue prolapse. Other applications maydictate a desired degree of stiffness in the center to reduce thelikelihood of breakage and impart the desired degree of softness at theend to allow for the best fit with the anatomy of the target area. Otherapplications may dictate that one or more of the rows be provided withcells that are sized larger than the cells in the remaining rows of thestent so as to provide access to a side branch in the lumen, e.g., forintroducing a second stent through one of the larger sized cells so asto permit construction of a bifurcated stent within the lumen. Stillanother application may dictate that one or more of the rows be providedwith cells which are adapted or modified so that upon expansion of thestent the portion of the stent defined by the adapted or modified row orrows has a diameter that is either larger or smaller than the remainingportions of the stent to accommodate lumens with non-uniform diameters.One or more rows of cells may also be adapted or modified so as to havevarying radial force, or varying longitudinal flexibility, or to correctfor a change in properties at the end of the stent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of the basic pattern of an embodiment ofthe stent of the present invention, shown in an unexpanded state;

FIG. 2 shows an illustration of the pattern of the stent of FIG. 1, in apartially expanded state;

FIG. 3 is a side view showing a conventional stent and a stentmanufactured in accordance with one embodiment of the invention;

FIG. 4 shows the stents of FIG. 3 crimped on a balloon catheter and bentprior to expansion;

FIG. 5 shows the stents of FIG. 4 after they have been expanded in acurve;

FIG. 6 shows the stents of FIG. 3 partially expanded on a substantiallystraight balloon catheter;

FIG. 7 shows an alternative embodiment of the invention provided with ashortened C-shaped loop and in which two rows of cells are provided withthinner gauge U-shaped loops;

FIG. 8 shows the stent of FIG. 7 partially expanded on a substantiallystraight balloon catheter;

FIG. 9 shows the stent of FIG. 7 after it has been expanded on a curvedcatheter as it would be when inserted around a bend in a vessel;

FIG. 10 shows an alternative embodiment of a stent constructed inaccordance with the invention; and

FIG. 11 shows the “S” or “Z” shaped loops constructed in accordance withthe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the general configuration of one embodiment of a stent 1fabricated in accordance with the present invention. The stent 1 may befabricated of bio-compatible materials such as stainless steel 316L,gold, tantalum, nitinol or other materials well known to those skilledin the art as suitable for this purpose. The dimensions and gauge ofmaterial utilized may be varied as specific applications dictate. Thestents of the present invention generally may be constructed in a mannerin accordance with the stent described in U.S. patent application Ser.No. 08/457,354, filed Jun. 1, 1995, the disclosure of which isincorporated herein by reference.

FIG. 1 is a side view of the distal end 2 of stent 1 of the presentinvention, showing the general pattern of the stent. As shown in FIGS. 1and 2 the pattern may be described as a plurality of cells 3 and 3′.Each cell 3 is provided with a first member 4, a second member 5, athird member 6, and a fourth member 7. A first C-shaped loop 10 isdisposed between the first member 4 and the third member 6 and a secondC-shaped loop 11 is disposed between the second member 5 and the fourthmember 7. In each of the cells 3, first member 4, second member 5, thirdmember 6, and fourth member 7 are substantially equal. Thus, firstC-shaped loop 10 is displaced a distance D1 and second C-shaped loop 11is displaced a distance D2 from the center of cell 3. In a preferredembodiment, D1 is substantially equal to D2. A first flexible connector8 is disposed between the first member 4 and the second member 5 and asecond flexible connector 9 is disposed between third member 6 andfourth member 7. The flexible connectors 8 and 9 may be made in avariety of shapes, e.g., an “S” or a “Z” shape as shown in FIG. 11. In apreferred embodiment, a “U” shape is utilized as shown in FIGS. 1 to 10.

FIG. 1 shows the pattern of stent 1 in an unexpanded state, i.e., thatstate in which the stent 1 is first inserted in a particular vessel inwhich a balloon angioplasty procedure is to be performed, but beforeballoon inflation. FIG. 2 shows the pattern of stent 1 in a partiallyexpanded state, i.e., that state after the balloon has been expanded,e.g. by a balloon, and the state in which the stent 1 remains in thevessel which it supports. The plurality of interconnected cells 3 and 3′form a plurality of interconnected rows 25, 26, 27, and 28 of cellsdisposed along the longitudinal axis of the stent 1. FIGS. 1 and 2 showa distal row 25 disposed at the distal end 2, a row 26 adjacent to andproximal to distal row 25, a row 27 adjacent to and proximal to row 26,and a row 28 adjacent to and proximal to row 27. It will be appreciatedthat the number of rows, and the number of cells per row, and the shapeof each cell, may be varied as specific applications require.

As shown in FIGS. 1 and 2, the cells 3′ in distal row 25 differ from thecells 3 in rows 26, 27, and 28. The first member 4′ and the third member6′ of the cells 3′ in row 25 are shorter than the first member 4 and thethird member 6 of the cells 3 in rows 26, 27 and 28. In cell 3′, firstmember 4′ is substantially equal to third member 6′, however, firstmember 4′ and third member 6′ are shorter than second member 5′ andfourth member 7′. The shorter members 4′ and 6′ result in a firstC-shaped loop 10′ that is not disposed as far away from the center ofthe cell 3′ as second C-shaped loop 11′. Thus, first C-shaped loop 10′may be thought of as being “shorter” than second C-shaped loop 11′. Asshown in FIG. 2, first C-shaped loop 10′ is disposed a distance D1′ thatis less than the distance D2′ that second C-shaped loop 11′ is disposedfrom the center of the cell 3′. In an especially preferred embodiment,D1′ is about 15% less than D2′.

FIGS. 1 and 2 also show that the distal row 25 of the stent 1 isprovided with a first U-shaped loop 8′ and a second U-shaped loop 9′that are more flexible than the first U-shaped loop 8 and secondU-shaped loop 9 of cells 3 in rows 26, 27, and 28 of the stent 1. Thisgreater flexibility in the U-shaped loops 8′ and 9′ may be accomplishedin a variety of ways, for example, by utilizing a different material, bytreating the material e.g., by utilizing stainless steel annealing toimpart selective degrees of hardness to the different portions of thestent. Alternatively, if, e.g., NiTi (Nitinol) is utilized, selectedportions of the stent may be selectively thermo-mechanically treated sothat portions of the stent, e.g., the U-shaped members, will remain in amartensitic phase while other portions of the stent will be transformedinto austenitic phase in this section to yield different properties.Greater flexibility may also be achieved by changing the shape of the“U”, for example to a “Z” or an “S” (as shown in FIG. 11), or byreducing the amount of material utilized to make the U-shaped loops 8′and 9′. In the embodiment shown in FIGS. 1 and 2, the U-shaped loops 8′and 9′ of row 25 are provided with the same thickness of material as theU-shaped loops 8 and 9 of the cells 3 in rows 26, 27, and 28, however,U-shaped loops 8′ and 9′ are not as wide. As shown in FIGS. 1 and 2,U-shaped loops 8′ and 9′ have a width W1 that is less than the width W2of U-shaped loops 8 and 9 in the cells 3 of rows 26, 27, and 28. In apreferred embodiment, W1 is about 50% narrower than W2. In an especiallypreferred embodiment, W1 is about 40% narrower than W2.

FIG. 3 is a side-by-side comparison of two stent sections and shows aconventional stent 12 compared to the stent 1, shown in FIGS. 1 and 2.FIG. 4 shows stents 1 and 12 shown in FIG. 3 as they appear when theyare crimped on a balloon and bent as they would be during insertionaround a curve in a vessel. As shown in FIG. 4, conventional stent 12flares at its leading edge 13 in contrast to stent 1 which does not.FIG. 5 shows the stents of FIG. 4 after the stents have been expanded ina curve. The tip of conventional stent 12 produces a protrusion or sharppoint 13 which could cause local pressure and possible trauma to thevessel wall. In contrast, the stent 1 constructed in accordance with theinvention bends gently at its end 2 without forming a protrusion orsharp point because the deformation of the of U-shaped loops 8′ and 9′in distal row 25 make the end 2 softer.

FIG. 6 shows the stents 1 and 12 of FIG. 3 at partial expansion (beforereaching maximum pressure) disposed on a substantially straightcatheter. As shown, although the two stents 1 and 12 are subjected tothe same outward force, the end 2 of stent 1 is less expanded than theend 13 of conventional stent 12 demonstrating the increased radial forceof the end 2 of stent 1 constructed in accordance with the invention. Atfull pressure the radii of the stents 1 and 12 will be equal, however,the end 2 of stent 1 will have greater radial resistance to collapsethan the end 13 of stent 12.

FIG. 7 shows an alternative embodiment of the invention. As shown inFIG. 7, the cells 3′ in row 25 are provided with a first member 4′ andthird member 6′ that are shorter than second member 5′ and fourth member7′. The cells 3′ in row 25 are provided with a first U-shaped loop 8′and a second U-shaped loop 9′ that are thinner than the U-shaped loops 8and 9 in the cells 3 in rows 27 and 28. The cells 3″ in row 26 areprovided with first U-shaped loops 8″ and second U-shaped loops 9″ thatare narrower than the U-shaped loops 8 and 9 in the cells 3 in rows 27and 28.

FIG. 8 shows the stent 20 of FIG. 7 during partial expansion of thestent showing the decreased expansion of row 25 at partial expansionbecause of the higher radial force of the end 2 of the stent whichresults from construction with shorter C-shaped loops 10′ in row 25,construction with narrower, i.e., more flexible, U-shaped loops 8′ and9′ in row 25, and 8″ and 9″ in row 26.

FIG. 9 shows the stent 20 of FIGS. 7 and 8 after it has been expanded ina curved vessel and shows the bends of the U-shaped loops 8′ and 9′ inrow 25 and 8″ and 9″ in row 26 which allows the end portion 2 of thestent 20 to more readily conform to the curve of the vessel, creatingsmooth ends with no sharp points or projections projecting into thevessel wall.

The changes can be made on one side only or on both sides of the stentas specific applications dictate. Additionally, different combinationsof embodiments of the invention may be mixed such as using thinnerU-shaped loops, longer U-shaped loops or different shaped loops, e.g.,“Z” or “S”.

One example of how this may be achieved is shown in FIG. 10. FIG. 10shows how the stent shown in FIG. 7 may be modified, if additionalflexibility is desired. As shown in FIG. 10, the distal row 25, and theproximal row 29 of stent 30 are provided with first and second U-shapedloops that are more flexible than the U-shaped loops in the other rowsof the stent disposed between the distal and proximal rows 25 and 29. Inthe embodiment of the invention shown in FIG. 10, the distal row 25 isprovided with shortened members 4′ and 6′ and more flexible U-shapedloops 8′ and 9′, as previously discussed, and the proximal row 29 isprovided with shortened second and fourth members 5″ and 7″ and moreflexible U-shaped loops 8′″ and 9′″. This arrangement imparts greaterradial strength and greater flexibility to both ends of the stent.

If even greater flexibility at the ends of the stent is desired, thestent shown in FIG. 10 may be modified by replacing the U-shaped loopsin rows 26 and 28 with more flexible loops. Thus, the distal row, therow proximal to the distal row, the proximal row, and the row distal tothe proximal row are provided with U-shaped loops that are more flexiblethan the U-shaped loops in the cells in the remaining rows of the stent.

The present invention contemplates a number of different variations andchanges in different properties to achieve other non uniform featuressuch as, but not limited to, cell size, cell shape, radio-opacity, etc.on the above-described preferred embodiments. The specified changes arebrought only as an example for the application of the general concept,which is the basis for the present invention that stents with varyingmechanical properties between sections along the stent may correctundesired effects at singular points such as stent ends and provide fora better fit to a vessel with properties changing along its axis. It isto be understood that the above description is only of one preferredembodiment, and that the scope of the invention is to be measured by theclaims as set forth below.

1. An expandable stent, comprising: a) a plurality of interconnectedflexible cells defining a stent having a proximal end and a distal endand a longitudinal axis, the cells arranged in a plurality ofinterconnected flexible rows disposed along the longitudinal axis of thestent with a distal row disposed at the distal end of the stent and aproximal row disposed at the proximal end of the stent, each of theflexible cells comprising a first member, a second member, a thirdmember and, a fourth member; b) a first C-shaped loop disposed betweenthe first member and the third member; c) a second C-shaped loopdisposed between the second member and the fourth member; d) a firstflexible connector disposed between the first member and the secondmember; and e) a second flexible connector disposed between the thirdmember and the fourth member, wherein the cells of the distal row havefirst and third members that are shorter than the second and fourthmembers.
 2. The stent of claim 1, wherein the first and the thirdmembers in the cells of the distal row are about 15% shorter than thesecond and the fourth members.
 3. An expandable stent, comprising: a) aplurality of interconnected flexible cells defining a stent having aproximal end and a distal end and a longitudinal axis, the cellsarranged in a plurality of interconnected flexible rows disposed alongthe longitudinal axis of the stent with a distal row disposed at thedistal end of the stent and a proximal row disposed at the proximal endof the stent, each of the flexible cells comprising a first member, asecond member, a third member and, a fourth member; b) a first C-shapedloop disposed between the first member and the third member; c) a secondC-shaped loop disposed between the second member and the fourth member;d) a first flexible connector disposed between the first member and thesecond member; and e) a second flexible connector disposed between thethird member and the fourth member, wherein the cells of the proximalrow have second and fourth members that are shorter than the first andthird members.
 4. The stent of claim 3, wherein the second and thefourth members in the cells of the proximal row are about 15% shorterthan the first and the third members.
 5. An expandable stent comprising:a) a plurality of flexible cells defining a stent having a proximal endand a distal end and a longitudinal axis, the cells arranged in aplurality of flexible rows along the longitudinal axis with a distal rowof cells disposed at the distal end of the stent and a proximal row ofcells disposed at the proximal end of the stent, each of the flexiblecells comprising a first member, a second member, a third member, and afourth member; b) a first C-shaped loop disposed between the firstmember and the third member; c) a second C-shaped loop disposed betweenthe second member and the fourth member; d) a first flexible connectordisposed between the first member and the second member; and e) a secondflexible connector disposed between the third member and the fourthmember, wherein the cells of the distal row have first and third membersthat are shorter than the second and fourth members, and wherein thecells of the proximal row have second and fourth members that areshorter than the first and third members.
 6. An expandable stent,comprising a plurality of interconnected flexible cells defining a stenthaving a proximal end and a distal end and a longitudinal axis and whichwhen expanded in a lumen exerts radial force along its length againstthe lumen wall, the cells arranged in a plurality of interconnectedflexible rows disposed along the longitudinal axis of the stent with adistal row disposed at the distal end of the stent and a proximal rowdisposed at the proximal end of the stent, wherein the distal row ofcells exert greater radial force than each row of cells disposed betweenthe distal row and the proximal row of the stent.
 7. An expandablestent, comprising a plurality of interconnected flexible cells defininga stent having a proximal end and a distal end and a longitudinal axisand which when expanded in a lumen exerts radial force along its lengthagainst the lumen wall, the cells arranged in a plurality ofinterconnected flexible rows disposed along the longitudinal axis of thestent with a distal row disposed at the distal end of the stent and aproximal row disposed at the proximal end of the stent, wherein theproximal row of cells exert greater radial force than each row of cellsdisposed between the distal row and the proximal row of the stent.
 8. Anexpandable stent, comprising a plurality of interconnected flexiblecells defining a stent having a proximal end and a distal end and alongitudinal axis and which when expanded in a lumen exerts radial forcealong its length against the lumen wall, the cells arranged in aplurality of interconnected flexible rows disposed along thelongitudinal axis of the stent with a distal row disposed at the distalend of the stent and a proximal row disposed at the proximal end of thestent, wherein each of the distal row cells and the proximal row ofcells exert greater radial force than each row of cells disposed betweenthe distal row and the proximal row of the stent.
 9. An expandable stenthaving a proximal end, a distal end and a longitudinal axis, comprising:a) a plurality of first circumferential bands arranged along thelongitudinal axis of the stent, each first circumferential band defininga generally serpentine pattern comprising a plurality of strut membersand a plurality of loops; b) a second circumferential band disposed atleast at one end of the stent, each second circumferential band defininga generally serpentine pattern comprising a plurality of strut membersand a plurality of loops, wherein the strut members of each secondcircumferential band are shorter in length than the strut members ofeach first circumferential band; and c) a plurality of flexibleconnectors coupling adjacent circumferential bands.
 10. The stent ofclaim 9 where the strut members of each second circumferential band havea length in the longitudinal direction of the stent that is less thanthe length in the longitudinal direction of the strut members of eachfirst circumferential band.
 11. The stent of claim 9, wherein a secondcircumferential band is disposed at the distal end of the stent.
 12. Thestent of claim 9, wherein a second circumferential band is disposed atthe proximal end of the stent.
 13. The stent of claim 9, wherein asecond circumferential band is disposed at the distal end of the stentand a second circumferential band is disposed at the proximal end of thestent.
 14. An expandable stent, comprising: a) a plurality ofinterconnected flexible cells defining a stent having a proximalsection, a central section, a distal section and a longitudinal axis,the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with at least one rowof cells disposed in the distal section of the stent, at least one rowof cells disposed in the central section of the stent, and at least onerow of cells disposed in the a proximal section of the stent, each ofthe flexible cells comprising a first member, a second member, a thirdmember and, a fourth member; b) a first C-shaped loop disposed betweenthe first member and the third member; c) a second C-shaped loopdisposed between the second member and the fourth member; d) a firstflexible connector disposed between the first member and the secondmember; and e) a second flexible connector disposed between the thirdmember and the fourth member, wherein the first and second flexibleconnectors in the cells of the at least one row of cells in the distalsection of the stent are more flexible than the first and secondflexible connectors in the cells of the at least one row of cells in thecentral section of the stent.
 15. The stent of claim 14, wherein the atleast one row of cells in the distal section comprises one row of cells.16. The stent of claim 14, wherein the at least one row of cells in thedistal section of the stent comprises two rows of cells.
 17. The stentof claim 14, wherein the first and second flexible connectors in thecells of the at least one row of cells in the distal section and thefirst and second flexible connectors in the cells of the at least onerow of cells in the proximal section are more flexible than the firstand second flexible connectors in the cells of the at least one row ofcells in the central section of the stent.
 18. The stent of claim 17,wherein the at least one row of cells in the distal section comprisesone row of cells and the at least one row of cells in the proximalsection comprises one row of cells.
 19. The stent of claim 17, whereinthe at least one row of cells in the distal section comprises two rowsof cells and the at least one row of cells in the proximal sectioncomprises two rows of cells.
 20. An expandable stent, comprising: a) aplurality of interconnected flexible cells defining a stent having aproximal section, a central section, a distal section and a longitudinalaxis, the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with at least one rowof cells disposed in the distal section of the stent, at least one rowof cells disposed in the central section of the stent and at least onerow of cells disposed in the proximal section of the stent, each of theflexible cells comprising a first member, a second member, a thirdmember and, a fourth member; b) a first C-shaped loop disposed betweenthe first member and the third member; c) a second C-shaped loopdisposed between the second member and the fourth member; d) a firstflexible connector disposed between the first member and the secondmember; and e) a second flexible connector disposed between the thirdmember and the fourth member, wherein the first and second flexibleconnectors in the cells of the at least one row of cells in the distalsection are narrower than the first and the second flexible connectorsin the cells of the at least one row of cells in the central section ofthe stent.
 21. The stent of claim 20, wherein the at least one row ofcells in the distal section comprises one row of cells.
 22. The stent ofclaim 20, wherein the at least one row of cells in the distal section ofthe stent comprises two rows of cells.
 23. The stent of claim 20,wherein the first and second flexible connectors in the cells of the atleast one row of cells in the distal section and the first and secondflexible connectors in the cells of the at least one row of cells in theproximal section are more narrower than the first and second flexibleconnectors in the cells of the at least one row of cells in the centralsection of the stent.
 24. The stent of claim 23, wherein the at leastone row of cells in the distal section comprises one row of cells andthe at least one row of cells in the proximal section comprises one rowof cells.
 25. The stent of claim 23, wherein the at least one row ofcells in the distal section comprises two rows of cells and the at leastone row of cells in the proximal section comprises two rows of cells.26. The stent of claim 20, wherein the first and the second flexibleconnectors in the cells of the at least one row of cells in the distalsection are about 40% narrower than the first and the second flexibleconnectors in the cells of the at least one row of cells in the centralsection of the stent.
 27. An expandable stent, comprising: a) aplurality of interconnected flexible cells defining a stent having aproximal section, a central section, a distal section and a longitudinalaxis, the cells arranged in a plurality of interconnected flexible rowsdisposed along the longitudinal axis of the stent with at least one rowof cells disposed in the distal section of the stent, at least one rowof cells disposed in the central section of the stent and at least onerow of cells disposed in the proximal section of the stent, each of theflexible cells comprising a first member, a second member, a thirdmember and, a fourth member; b) a first C-shaped loop disposed betweenthe first member and the third member; c) a second C-shaped loopdisposed between the second member and the fourth member; d) a firstflexible connector disposed between the first member and the secondmember; and e) a second flexible connector disposed between the thirdmember and the fourth member, wherein the first and second flexibleconnectors in the cells of the at least one row of cells in the distalsection are formed of a smaller gauge material than the material of thefirst and the second flexible connectors in the cells of the at leastone row of cells in the central section of the stent.
 28. The stent ofclaim 27, wherein the at least one row of cells in the distal sectioncomprises one row of cells.
 29. The stent of claim 27, wherein the atleast one row of cells in the distal section of the stent comprises tworows of cells.
 30. The stent of claim 27, wherein the first and secondflexible connectors in the cells of the at least one row of cells in thedistal section and the first and second flexible connectors in the cellsof the at least one row of cells in the proximal section are formed of asmaller gauge material than the material of the first and secondflexible connectors in the cells of the at least one row of cells in thecentral section of the stent.
 31. The stent of claim 30, wherein the atleast one row of cells in the distal section comprises one row of cellsand the at least one row of cells in the proximal section comprises onerow of cells.
 32. The stent of claim 30, wherein the at least one row ofcells in the distal section comprises two rows of cells and the at leastone row of cells in the proximal section comprises two rows of cells.33. An expandable stent, comprising: a) a plurality of interconnectedflexible cells defining a stent having a proximal section, a centralsection, a distal section and a longitudinal axis, the cells arranged ina plurality of interconnected flexible rows disposed along thelongitudinal axis of the stent with at least one row of cells disposedin the distal section of the stent, at least one row of cells disposedin the central section of the stent, and at least one row of cellsdisposed in the a proximal section of the stent, each of the flexiblecells comprising a first member, a second member, a third member and, afourth member; b) a first C-shaped loop disposed between the firstmember and the third member; c) a second C-shaped loop disposed betweenthe second member and the fourth member; d) a first flexible connectordisposed between the first member and the second member; and e) a secondflexible connector disposed between the third member and the fourthmember, wherein the first and second flexible connectors in the cells ofthe at least one row of cells in the proximal section of the stent aremore flexible than the first and second flexible connectors in the cellsof the at least one row of cells in the central section of the stent.34. The stent of claim 33, wherein the at least one row of cells in theproximal section comprises one row of cells.
 35. The stent of claim 33,wherein the at least one row of cells in the proximal section of thestent comprises two rows of cells.
 36. An expandable stent, comprising:a) a plurality of interconnected flexible cells defining a stent havinga proximal section, a central section, a distal section and alongitudinal axis, the cells arranged in a plurality of interconnectedflexible rows disposed along the longitudinal axis of the stent with atleast one row of cells disposed in the distal section of the stent, atleast one row of cells disposed in the central section of the stent andat least one row of cells disposed in the proximal section of the stent,each of the flexible cells comprising a first member, a second member, athird member and, a fourth member; b) a first C-shaped loop disposedbetween the first member and the third member; c) a second C-shaped loopdisposed between the second member and the fourth member; d) a firstflexible connector disposed between the first member and the secondmember; and e) a second flexible connector disposed between the thirdmember and the fourth member, wherein the first and second flexibleconnectors in the cells of the at least one row of cells in the proximalsection are narrower than the first and the second flexible connectorsin the cells of the at least one row of cells in the central section ofthe stent.
 37. The stent of claim 36, wherein the at least one row ofcells in the proximal section comprises one row of cells.
 38. The stentof claim 36, wherein the at least one row of cells in the proximalsection of the stent comprises two rows of cells.
 39. The stent of claim36, wherein the first and the second flexible connectors in the cells ofthe at least one row of cells in the proximal section are about 40%narrower than the first and the second flexible connectors in the cellsof the at least one row of cells in the central section of the stent.40. An expandable stent, comprising: a) a plurality of interconnectedflexible cells defining a stent having a proximal section, a centralsection, a distal section and a longitudinal axis, the cells arranged ina plurality of interconnected flexible rows disposed along thelongitudinal axis of the stent with at least one row of cells disposedin the distal section of the stent, at least one row of cells disposedin the central section of the stent and at least one row of cellsdisposed in the proximal section of the stent, each of the flexiblecells comprising a first member, a second member, a third member and, afourth member; b) a first C-shaped loop disposed between the firstmember and the third member; c) a second C-shaped loop disposed betweenthe second member and the fourth member; d) a first flexible connectordisposed between the first member and the second member; and e) a secondflexible connector disposed between the third member and the fourthmember, wherein the first and second flexible connectors in the cells ofthe at least one row of cells in the proximal section are formed of asmaller gauge material than the material of the first and the secondflexible connectors in the cells of the at least one row of cells in thecentral section of the stent.
 41. The stent of claim 40, wherein the atleast one row of cells in the distal section comprises one row of cells.42. The stent of claim 40, wherein the at least one row of cells in thedistal section of the stent comprises two rows of cells.
 43. Anexpandable stent having a proximal section, a central section, a distalsection and a longitudinal axis, comprising: a) a plurality ofcircumferential bands arranged along the longitudinal axis of the stent,each circumferential band defining a generally serpentine patterncomprising a plurality of strut members and a plurality of loops,wherein at least two circumferential bands are disposed in the proximalsection of the stent, at least two circumferential bands are disposed inthe central section of the stent and at least two circumferential bandsare disposed in the distal section of the stent; and b) a plurality offlexible connectors coupling adjacent circumferential bands, wherein theflexible connectors coupling the at least two circumferential bandsdisposed in the distal section of the stent are more flexible than theflexible connectors coupling the at least two circumferential bandsdisposed in the central section of the stent.
 44. The stent of claim 43,wherein the flexible connectors coupling the at least twocircumferential bands disposed in the distal section of the stent andthe flexible connectors coupling the at least two circumferential bandsdisposed in the proximal section of the stent are more flexible than theflexible connectors coupling the at least two circumferential bandsdisposed in the central section of the stent.
 45. The stent of claim 44,wherein the at least two circumferential bands disposed in the distalsection of the stent comprises two circumferential bands and the atleast two circumferential bands disposed in the proximal section of thestent comprises two circumferential bands.
 46. The stent of claim 44,wherein the at least two circumferential bands disposed in the distalsection of the stent comprises three circumferential bands and the atleast two circumferential bands disposed in the proximal section of thestent comprises three circumferential bands.
 47. An expandable stenthaving a proximal section, a central section, a distal section and alongitudinal axis, comprising: a) a plurality of circumferential bandsarranged along the longitudinal axis of the stent, each circumferentialband defining a generally serpentine pattern comprising a plurality ofstrut members and a plurality of loops, wherein at least twocircumferential bands are disposed in the proximal section of the stent,at least two circumferential bands are disposed in the central sectionof the stent and at least two circumferential bands are disposed in thedistal section of the stent; and b) a plurality of flexible connectorscoupling adjacent circumferential bands, wherein the flexible connectorscoupling the at least two circumferential bands disposed in the proximalsection of the stent are more flexible than the flexible connectorscoupling the at least two circumferential bands disposed in the centralsection of the stent.
 48. An expandable stent for implanting in a lumenhaving variable characteristics, the expandable stent having a distalend, a proximal end and a longitudinal axis and comprising a pluralityof flexible cells arranged in a plurality of flexible rows disposedalong the longitudinal axis of the stent, wherein at least one flexiblerow of cells has physical properties to accommodate the characteristicsof the portion of the lumen with which the at least one flexible row ofcells is in contact when the stent is implanted in the lumen.
 49. Theexpandable stent of claim 48, wherein the lumen variable characteristicscomprise an ostium and the at least one flexible row of cells of thestent in contact with the ostium when the stent is implanted in thelumen has increased radial strength relative to that of at least oneother flexible row of cells of the stent.
 50. The expandable stent ofclaim 48, wherein the lumen variable characteristics comprise acurvature and the at least one flexible row of cells of the stent incontact with the curvature when the stent is implanted in the lumen hasincreased flexibility relative to that of at least one other flexiblerow of cells of the stent.
 51. The expandable stent of claim 48, whereinthe lumen variable characteristics comprise a non-uniform lumen diameterand each of the flexible rows of cells is dimensioned to accommodate thediameter of the portion of the lumen with which it is in contact whenthe stent is implanted in the lumen.
 52. The expandable stent of claim48, wherein the lumen variable characteristics comprise a non-uniformlumen cross-section and each of the flexible rows of cells isdimensioned to accommodate the cross-section of the portion of the lumenwith which it is in contact when the stent is implanted in the lumen.53. An expandable stent having a distal end, a proximal end and alongitudinal axis and comprising a plurality of flexible cells arrangedin a plurality of flexible rows disposed along the longitudinal axis ofthe stent, wherein at least one flexible row of cells has at least onecell that is larger than the cells of at least one other flexible row ofcells to provide access to insert a second stent into a side branch inthe lumen.
 54. A expandable stent, comprising, in its expandedcondition: a plurality of interconnected flexible cells defining a stenthaving a proximal end, a central section and a distal end and alongitudinal axis, the cells arranged in a plurality of interconnectedflexible rows disposed along the longitudinal axis of the stent with atleast one distal row disposed at the distal end of the stent and atleast one proximal row disposed at the proximal end of the stent,wherein the cells disposed in the at least one row at an end of thestent exert greater radial force and are more flexible than the cellsdisposed in the rows in the central section.
 55. The stent of claim 54wherein the cells disposed in the at least one distal row of the stentexert greater radial force and are more flexible than the cells disposedin the rows in the central section.
 56. The stent of claim 55, whereincells in the most distal row and the row proximal to the most distal rowof the stent exert greater radial force and are more flexible than thecells disposed in the rows in the central section.
 57. The stent ofclaim 56 wherein the cells disposed in the at least one proximal row ofthe stent exert greater radial force and are more flexible than thecells disposed in the rows in the central section.
 58. The stent ofclaim 57, wherein cells in the most distal row and the row proximal tothe most distal row of the stent and the cells in the most proximal rowand the row distal to the most proximal row of the stent exert greaterradial force and are more flexible than the cells disposed in the rowsin the central section.
 59. The stent of claim 54 wherein the cellsdisposed in the at least one proximal row of the stent exert greaterradial force and are more flexible than the cells disposed in the rowsin the central section.
 60. The stent of claim 59, wherein cells in themost proximal row and the row distal to the most proximal row of thestent exert greater radial force and are more flexible than the cellsdisposed in the rows in the central section.
 61. A expandable stent,comprising in its expanded condition: a plurality of interconnectedflexible cells defining a stent having a proximal end, a central sectionand a distal end and a longitudinal axis, the cells arranged in aplurality of interconnected flexible rows disposed along thelongitudinal axis of the stent with at least one distal row disposed atthe distal end of the stent and at least one proximal row disposed atthe proximal end of the stent, wherein the cells disposed in the atleast one row at an end of the stent are more flexible than the cellsdisposed in the rows in the central section.
 62. The stent of claim 61wherein the cells disposed in the at least one distal row of the stentare more flexible than the cells disposed in the rows in the centralsection.
 63. The stent of claim 62, wherein cells in the most distal rowand the row proximal to the most distal row of the stent are moreflexible than the cells disposed in the rows in the central section. 64.The stent of claim 63 wherein the cells disposed in the at least oneproximal row of the stent are more flexible than the cells disposed inthe rows in the central section.
 65. The stent of claim 64, whereincells in the most distal row and the row proximal to the most distal rowof the stent and the cells in the most proximal row and the row distalto the most proximal row of the stent are more flexible than the cellsdisposed in the rows in the central section.
 66. The stent of claim 61wherein the cells disposed in the at least one proximal row of the stentare more flexible than the cells disposed in the rows in the centralsection.
 67. The stent of claim 66, wherein cells in the most proximalrow and the row distal to the most proximal row of the stent are moreflexible than the cells disposed in the rows in the central section.